1. Field of the Invention
This invention relates to float controlled valves of the type widely used to control the level to which cisterns, reservoirs, animal drinking troughs and the like are replenished automatically from a supply of liquid under pressure.
2. Description of the Prior Art
Water pressure variations in the water controlled by the valve cause problems if the variations are extreme and there is a need for a valve which can cope with these and still be economically made.
The inefficient mechanical advantage of the lever in conventional float arm closing mean is such that if the float arm is bent to set the water level at the comparatively lower mains pressures which prevail in the daylight hours due to the water usage being high, it will be found that the level of the liquid will be very much higher during quiet or low consumption periods such as at night or early morning. This is because the float has to be submerged to a greater extent and only this greater displacement can cause the float to seal the float valve at higher pressures.
This cannot be accomplished however, without a considerable rise in the water level which will be far beyond the desired liquid level of the cistern or container resulting in many cases in continual overflowing during these high pressure periods. Conversely, if the float valve is set to a pre-determined level during peak pressure periods it follows that during low pressure or high offtake periods a cistern or container will only fill to a lower level and in a cistern will render efficient flushing impossible. Flushing cisterns operate efficiently at suitable predetermined water levels only.
Water supply authorities also demand a non-return or back syphonage prevention facility in float valves so that pollution of the water supply pipes from a cistern or trough cannot occur.
Float controlled valves which are presently available often have the attendant disadvantage that a separate stop valve must be provided for the supply inlet to the valve. This is necessary so that the float controlled valve can be isolated from the mains supply for servicing it.